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Math Help - Logarithms

  1. #1
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    Logarithms

    Suppose that for some values of A and r, P(t)=Aⅇ^(rt) and we know that P(3)=250 and P(11)=2P(0). Find P(7).

    I have no clue how to even start this.
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  2. #2
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    Quote Originally Posted by velvet love View Post
    suppose that for some values of a and r, p(t)=aⅇ^(rt) and we know that p(3)=250 and p(11)=2p(0). Find p(7).

    I have no clue how to even start this.
    Given p(11)=p(0)=a^0=1

    since p(11) = a^{11r}=1, 11r=a\rightarrow r=\frac{a}{11}

    Plug r=\frac{a}{11} into P(t). You will get P(t)=a^{\frac{a}{11}t}

    Now, p(3)=a^{\frac{3a}{11}}=250 \rightarrow\frac{3a}{11}= a^{250}

    Then take log of bothsides:
    \log{3a}-\log{11}= 250\log{a}

    You should be able to do the rest. You might want to check my algebra for I must go back to my work now. I'll catch up with you later.
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  3. #3
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    I think i typed the original equation wrong.
    its supposed to be Ae^(rt).
    And p(11) = 2*p(0)
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  4. #4
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    Quote Originally Posted by Velvet Love View Post
    I think i typed the original equation wrong.
    its supposed to be Ae^(rt).
    And p(11) = 2*p(0)
    Alright, let's try again.

    p(11)=2p(0) \rightarrow Ae^{11r}= Ae^0 \rightarrow  Ae^{11r}= A\rightarrow e^{11r}= 1\rightarrow
    11r\ln e= ln1\rightarrow  11r= ln1\rightarrow r= \frac{\ln1}{11}

    Now plug r into and t= 7 or whatever number to find the value of the function.

    I don't have very good eye. I might have made mistakes when in a hurry going out the door. You might want to double check and triple chech my algebra. It would be best you take some time to review and practice your logarithm again. I understand you are underpressure.
    Last edited by novice; October 12th 2009 at 03:19 PM. Reason: typo
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